JP2970289B2 - Zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a lens group having a negative refractive power, which has three lens groups as a whole. The present invention relates to a zoom lens suitable for a small-sized and wide-angle still camera or a video camera.

[0002]

2. Description of the Related Art Conventionally, a zoom lens in which the total length of the lens is shortened and the lens outer shape is reduced is disclosed in
These are proposed in Japanese Patent Application Laid-Open No. 9-142515, Japanese Patent Application Laid-Open No. 59-64811, and the like.

[0003] These publications disclose a so-called short zoom lens having two lens units, a first unit having a negative refractive power and a second unit having a positive refractive power, and performing zooming by changing the distance between both lens units. is suggesting.

[0004] Short zoom lenses are often used in single-lens reflex cameras because a predetermined back focus can be relatively easily secured even if the focal length is set shorter than the screen size.

In a short zoom lens, a so-called three-group zoom lens is provided in which a third lens group having a positive or negative refractive power is newly disposed on the image plane side to shorten the overall length of the lens while securing a predetermined zoom ratio. For example, it has been proposed in Japanese Patent Application Laid-Open Nos. 58-9016 and 58-111013.

In a three-unit zoom lens, a lens having high optical performance over the entire zoom range while achieving high zoom ratio by appropriately setting the refractive power and the lens configuration of each lens unit is known. JP-A-61-183613,
JP-A-61-240217, JP-A-62-879
No. 25, JP-A-62-112115 and JP-A-1-189622.

A wide-angle zoom lens having a wide-angle end angle of view of 90 degrees or more has been proposed in Japanese Patent Application Laid-Open No. 58-5707.

Also, a short zoom lens and negative, positive,
Japanese Patent Application Laid-Open No. Hei 2-201310 has proposed a four-group zoom lens including four lens groups having negative and positive refractive powers.

[0009]

In general, a zoom type in which a lens unit having a negative refractive power is preceded, in order to secure a predetermined back focus and to shorten the entire length of the lens while keeping the lens diameter small, it is necessary to add a lens unit to each lens unit. A strong refractive power must be given.

However, when the refractive power of each lens unit is increased, deterioration of the peripheral portion of the image on the wide-angle side, that is, in other words, aberration, in other words, curvature of field, astigmatism, and distortion are significantly increased. Further, on the telephoto side, many high-order spherical aberrations and astigmatism are generated, and it is difficult to satisfactorily correct them. In particular, astigmatism on the telephoto side tends to be excessive at a low angle of view, and excessively low at a high angle of view.

In JP-A-58-5707 and JP-A-2-201310, aberration correction is performed by using an aspherical surface in the front group having a negative refractive power. When correcting aberrations using an aspherical surface, it is important to appropriately set the lens surface on which the aspherical surface is to be applied, in order to sufficiently obtain the effect of the aspherical surface.

In the three-unit zoom lens, the negative refracting power of the front unit cannot be increased beyond the limit in terms of aberration correction. As a result, there has been a problem that the distance to the stop becomes large and the peripheral light amount cannot be sufficiently secured unless the diameter of the front lens is increased. For this reason, when trying to widen the angle of view with a three-group zoom lens, the entire lens system tends to be large.

In general, when the size of the entire lens system is increased, for example, a lens group having a large diameter and a large weight must be driven during autofocusing, which is extremely disadvantageous in terms of driving force and driving speed.

According to the present invention, in a zoom lens having three lens groups as a whole having a predetermined refractive power, by appropriately specifying the refractive power and the lens configuration of each lens group, aberration variation accompanying zooming is small, and It is an object of the present invention to provide a zoom lens having a high optical performance over a wide range, a wide angle of view, and a short lens length suitable for a photographic camera or a video camera.

[0015]

The zoom lens according to the present invention comprises (1-1) a first unit having a negative refractive power, a second unit having a negative refractive power, and a third unit having a positive refractive power in order from the object side. When performing zooming by moving the second and third units on the optical axis, the first unit includes a positive meniscus eleventh lens with a convex surface facing the object side. A lens and a meniscus negative twelfth lens having a convex surface facing the object side, and the second group includes at least one negative lens and a meniscus positive lens having a convex surface facing the object side. When the refractive indices of the materials of the eleventh lens and the twelfth lens are N11 and N12, respectively, N11 <N12 is satisfied.

[0016]

1 to 3 are sectional views of the zoom lens according to the present invention at the wide-angle end in numerical examples 1 to 3 which will be described later.

FIGS. 4 to 6 are aberration diagrams at a photographing magnification of -0.02 times at the wide-angle end, middle, and telephoto end of Numerical Embodiment 1 of the present invention, and FIGS. 7 to 9 are Numerical Embodiment 2 of the present invention. FIGS. 10 to 12 show aberrations at a wide-angle end, a middle position, and a telephoto end at a photographing magnification of -0.02 times at the wide-angle end, a middle position, and a telephoto end. FIG.

In the figure, L1 is a first group having a negative refractive power, L2 is a second group having a positive refractive power, L3 is a third group having a negative refractive power, SP is an aperture stop, and FP is an image plane.

Next, numerical examples 1 and 2 shown in FIGS.
A few zoom lenses will be described.

The zoom lenses of Numerical Embodiments 1, 2, and 3 have a first group of negative refractive power and a second group of negative refractive power in order from the object side.
The third lens group has a positive refractive power and a third lens group. At the time of zooming from the wide-angle end to the telephoto end, the third unit is moved to the object side as shown by the arrow to perform zooming, and the image plane fluctuation accompanying the zooming is reciprocated with the second unit corresponding thereto. It has been corrected. Focusing is performed by moving the second lens unit.

As described above, in the first, second, and third numerical embodiments, the second lens unit and the third lens unit are moved as described above at the time of zooming, and the first lens unit is the first meniscus positive first lens whose convex surface faces the object side.
The second group includes one lens and a negative meniscus twelfth lens having a convex surface facing the object side, and the second group includes at least one negative lens and a positive meniscus lens having a convex surface facing the object side.

More specifically, the second group is composed of two meniscus negative lenses having a convex surface facing the object side and a meniscus positive lens having a convex surface facing the object side. By configuring the first group having a negative refractive power to include the two lenses having the above-described lens shapes, distortion and astigmatism which are significantly generated mainly on the wide-angle side are favorably corrected.

The second group having a negative refractive power is a compensator for compensating for image plane fluctuations caused by zooming, so that the function allocation is made independent. You can choose freely. This enables an arrangement in which the overall length and lens diameter of the lens are reduced, thereby making the entire lens system compact and favorably correcting aberrations.

The focusing may be performed by moving the first lens unit, or may be performed by moving the first lens unit and the second lens unit together or simultaneously at a predetermined ratio. In this embodiment, the second group, which is small and light, is used to facilitate the auto focus.

The second lens unit includes a negative lens and a positive meniscus lens. The second lens unit includes a lens structure that corrects spherical aberration that tends to occur mainly on the telephoto side, and corrects spherical aberration and coma aberration that fluctuate during focusing. I have.

It is preferable to use two negative lenses in the second lens unit, because it is possible to favorably correct curvature of field and astigmatism.

The third lens unit in the first and second numerical embodiments has a positive 31st lens having both lens surfaces convex, a stop, a positive 32nd lens having both convex lens surfaces, a negative 33rd lens and a 34th positive lens. It comprises a first cemented lens joined with a lens, a negative 35th meniscus lens having a convex surface facing the object side, a 36th positive lens, and a 37th positive lens.

Also, in Numerical Embodiment 3, both the lens surfaces are the positive 31st lens having a convex surface, the stop, and both lens surfaces are the positive 3rd lens having a convex surface.
It is composed of two lenses, a negative 33rd lens, a positive 34th lens, a negative 35th meniscus lens having a convex surface facing the object side, a 36th positive lens, and a 37th positive lens.

In Numerical Embodiment 3, the 33rd lens and the 34th lens are separated and an air lens is provided as compared with Numerical Embodiments 1 and 2, so that the spherical aberration and the sagittal halo at the periphery of the screen are improved. Has been corrected.

In Numerical Embodiments 1, 2, and 3, by setting each element as described above, the entire lens range is reduced from the wide angle of view to the standard zoom ratio of about 2 while shortening the overall length of the lens. A zoom lens having excellent optical performance has been obtained.

In the numerical examples 1, 2, and 3, the angle of view is about 93 ° to 65 ° and the F number is 3.5 to 4.5.

In the numerical examples 1, 2, and 3, (2-1) When the focal length of the i-th lens unit is fi, f3 <| f2 | <| f1 | (1) I have.

Conditional expression (1) is for appropriately setting the refractive power of each lens unit and reducing the overall length of the lens and the outer diameter of the lens.

In particular, the negative refractive power is assigned more to the second group than the first group, and the absolute value of the positive refractive power of the third group is made stronger than that of the first and second groups. The predetermined zooming is effectively performed with an extremely small amount of movement.

(2-2) Assuming that the refractive indexes of the materials of the eleventh lens and the twelfth lens are N11 and N12, respectively, N11 <N12 (2) ).

Conditional expression (2) is a condition for favorably correcting distortion and astigmatism mainly occurring on the wide-angle side. The distortion and the astigmatism are favorably corrected by increasing the curvature difference of the positive lens surface without increasing the refractive power of each lens surface of the negative lens of the first group. (2-3) 1.6 when the refractive index or average refractive index of the material of the negative lens of the second group and N2 _N <N2 _N ·················・ (3)

Conditional expression (3) is used to correct astigmatism, which tends to occur on the wide-angle side, by using a high-refractive-index negative lens in the second lens unit, and to satisfactorily correct distortion.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air spacing from the object side, and Ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples. Numerical Example 1 f = 20.60 to 34.09 fno = 1: 3.5 to 4.5 2 ω = 92.8 °
664.8 ° R 1 = 80.59 D 1 = 4.10 N 1 = 1.62299 ν 1 = 58.2 R 2 = 202.04 D 2 = 0.10 R 3 = 48.14 D 3 = 1.70 N 2 = 1.78590 ν 2 = 44.2 R 4 = 21.61 D 4 = Variable R 5 = 39.85 D 5 = 1.40 N 3 = 1.80610 ν 3 = 41.0 R 6 = 16.65 D 6 = 4.65 R 7 = 141.29 D 7 = 1.30 N 4 = 1.77250 ν 4 = 49.6 R 8 = 32.48 D 8 = 2.80 R 9 = 25.81 D 9 = 3.00 N 5 = 1.84666 ν 5 = 23.8 R10 = 70.11 D 10 = Variable R11 = 77.91 D 11 = 2.20 N 6 = 1.58313 ν 6 = 59.4 R12 = -77.90 D 12 = 1.78 R13 = (Aperture) D 13 = 0.92 R14 = 34.17 D 14 = 6.90 N 7 = 1.62606 ν 7 = 39.2 R15 = -39.89 D 15 = 3.50 R16 = -15.90 D 16 = 2.50 N 8 = 1.84666 ν 8 = 23.8 R17 = -417.04 D 17 = 3.80 N 9 = 1.78590 ν 9 = 44.2 R18 = -20.50 D 18 = 0.20 R19 = 82.47 D 19 = 1.20 N10 = 1.83400 ν10 = 37.2 R20 = 25.23 D 20 = 1.65 R21 = -111.96 D 21 = 2.50 N11 = 1.51633 ν11 = 64.2 R22 = -25.61 D 22 = 0.20 R23 = -343.40 D 23 = 2.15 N12 = 1.51633 ν12 = 64.2 R24 = -47.31

[0040]

[Table 1] Numerical example 2 f = 20.55 to 34.14 fno = 1: 3.5 to 4.5 2 ω = 92.9
° to 64.7 ° R 1 = 83.36 D 1 = 4.07 N 1 = 1.60311 ν 1 = 60.7 R 2 = 216.05 D 2 = 0.10 R 3 = 47.63 D 3 = 1.70 N 2 = 1.80610 ν 2 = 41.0 R 4 = 21.58 D 4 = Variable R 5 = 40.41 D 5 = 1.40 N 3 = 1.80610 ν 3 = 41.0 R 6 = 16.50 D 6 = 4.72 R 7 = 157.04 D 7 = 1.30 N 4 = 1.80400 ν 4 = 46.6 R 8 = 31.97 D 8 = 2.28 R 9 = 25.65 D 9 = 3.00 N 5 = 1.84666 ν 5 = 23.8 R10 = 89.80 D 10 = Variable R11 = 73.03 D 11 = 3.36 N 6 = 1.60311 ν 6 = 60.7 R12 = -78.75 D 12 = 1.78 R13 = (Aperture ) D 13 = 0.92 R14 = 33.46 D 14 = 7.12 N 7 = 1.58921 ν 7 = 40.9 R15 = -39.53 D 15 = 3.68 R16 = -15.90 D 16 = 2.54 N 8 = 1.84666 ν 8 = 23.8 R17 = -388.18 D 17 = 3.42 N 9 = 1.78590 ν 9 = 44.2 R18 = -20.52 D 18 = 0.20 R19 = 82.76 D 19 = 1.20 N10 = 1.83400 ν10 = 37.2 R20 = 25.65 D 20 = 1.65 R21 = -115.32 D 21 = 2.50 N11 = 1.60311 ν11 = 60.7 R22 = -25.76 D 22 = 0.20 R23 = -335.66 D 23 = 2.15 N12 = 1.60311 ν12 = 60.7 R24 = -69.47

[0041]

[Table 2] Numerical Example 3 f = 20.60 to 34.25 fno = 1: 3.5 to 4.5 2 ω = 92.8 °
664.6 ° R 1 = 81.48 D 1 = 4.14 N 1 = 1.60311 ν 1 = 60.7 R 2 = 213.04 D 2 = 0.10 R 3 = 48.41 D 3 = 1.70 N 2 = 1.80610 ν 2 = 41.0 R 4 = 21.57 D 4 = Variable R 5 = 39.84 D 5 = 1.40 N 3 = 1.80610 ν 3 = 41.0 R 6 = 16.43 D 6 = 4.79 R 7 = 170.12 D 7 = 1.30 N 4 = 1.80400 ν 4 = 46.6 R 8 = 32.61 D 8 = 2.07 R 9 = 25.25 D 9 = 3.00 N 5 = 1.84666 ν 5 = 23.8 R10 = 87.42 D 10 = Variable R11 = 72.78 D 11 = 3.56 N 6 = 1.60311 ν 6 = 60.7 R12 = -92.69 D 12 = 1.50 R13 = (Aperture) D 13 = 0.50 R14 = 34.93 D 14 = 7.16 N 7 = 1.58921 ν 7 = 40.9 R15 = -42.15 D 15 = 4.17 R16 = -14.67 D 16 = 1.94 N 8 = 1.80518 ν 8 = 25.4 R17 = 735.27 D 17 = 0.22 R18 = 368.24 D 18 = 2.59 N 9 = 1.78590 ν 9 = 44.2 R19 = -18.91 D 19 = 0.20 R20 = 90.59 D 20 = 1.40 N10 = 1.83400 ν10 = 37.2 R21 = 25.84 D 21 = 1.80 R22 = -115.83 D 22 = 2.60 N11 = 1.60311 ν11 = 60.7 R23 = -25.72 D 23 = 0.20 R24 = -228.15 D 24 = 2.00 N12 = 1.51633 ν12 = 64.2 R25 = -51.29

[0042]

[Table 3]

[0043]

[Table 4]

[0044]

According to the present invention, by specifying the refractive power and the lens configuration of the three lens groups as described above, the entire zoom ratio of about 2 with a wide field angle and a compact overall lens system is achieved. A compact zoom lens having good optical performance over the zoom range can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens at a wide angle end according to Numerical Embodiment 1 of the present invention.

FIG. 2 is a sectional view of a lens at a wide-angle end according to a second numerical embodiment of the present invention.

FIG. 3 is a sectional view of a lens at a wide-angle end according to a third numerical embodiment of the present invention;

FIG. 4 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 5 is an intermediate aberration diagram of the numerical example 1 of the present invention.

FIG. 6 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 7 is an aberration diagram at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 8 is an intermediate aberration diagram of the numerical example 2 of the present invention.

FIG. 9 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention;

FIG. 10 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 11 is an intermediate aberration diagram of the numerical example 3 of the present invention.

FIG. 12 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

[Explanation of symbols]

L ₁ first group L ₂ second group L ₃ third group SP aperture P flare stop FP image plane

Claims (3)

(57) [Claims] 1. A lens system comprising: a first lens unit having a negative refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power, in order from the object side. When zooming is performed by moving the third lens unit on the optical axis, the first lens unit includes a positive meniscus eleventh lens having a convex surface facing the object side and a negative meniscus negative lens having a convex surface facing the object side. The second group has at least one negative lens and a meniscus-shaped positive lens having a convex surface facing the object side, and has a refractive index of the material of the eleventh lens and the twelfth lens. N
11. A zoom lens, wherein N11 <N12, where N11 and N12. 2. The zoom lens according to claim 1, wherein f3 <| f2 | <| f1 | when the focal length of the i-th lens unit is fi. 3. A zoom lens according to claim 1, characterized in that a 1.6 <N2 _N and the refractive index or average refractive index of the material of the negative lens in the second group and N2 _N.